1. Field of the Invention
The invention relates to methods of polymerizing styrene. More particularly, it relates to methods of homogeneous polymerization of styrene based on an interactive initiation system.
2. Background
Since the discovery that rubber-like polymers of improved quality may be produced by polymerizations conducted at relatively low temperatures, numerous polymerization formulations and procedures have been developed to take advantage of this resulting quality improvement. Monomers benefiting from these polymerizations include, in particular, those that are ethylenically unsaturated, such as conjugated butadienes; haloprenes; alkenyl aromatic hydrocarbons such as styrene; acrylic and acrylic esters and their nitrites and amides; vinyl acetate; and the like. These monomers may be polymerized to form materials that are highly sought for a variety of uses, including durable goods, such as furniture, toys, housings, storage containers, and many others.
Unfortunately, reducing the temperature of polymerization in order to improve polymer quality may also result in undesired effects, such as reduced reproducibility, slower rate of reaction and increased induction time. To offset one or more of these disadvantages, a number of methods have been developed that frequently use relatively expensive initiators.
These procedures may be separated into two general categories: heterogeneous polymerizations, in which the initiator exists in a different phase from that of the reactants; and homogeneous, or “bulk”, polymerizations, in which the initiator exists in the same phase as that of the reactants. Heterogeneous polymerizations include emulsion polymerizations. Many emulsion polymerization systems employ redox initiators that are soluble in water, but not soluble in the monomer or monomer mix. These initiators may enable the polymerization to be carried out at relatively low temperatures, e.g., in some cases at or below room temperature. However, the water-soluble redox initiators tend to be expensive and the reaction rate and/or efficiency tends to be impractical from a commercial standpoint.
Thus, what is needed in the art is a method of homogeneously polymerizing unsaturated organic compounds that produces polymers of improved quality. Desirably, such a method would operate effectively at relatively low temperatures, but could employ relatively inexpensive initiators. It is also desirable that the method reduces or eliminates the occurrence of temperature-related problems, such as reduced reaction rates.